The stratum basale (basal layer, sometimes referred to as stratum germinativum) is the deepest layer of the five epidermis layers, which is the outer covering of skin in mammals.
The stratum basale is a continuous layer of cells. It is often described as one cell thick, though it may in fact be two to three cells thick in glabrous (hairless) skin and hyperproliferative epidermis (from a skin disease).
The stratum basale is primarily made up of basal keratinocyte stem cells, which can be considered the stem cells of the epidermis. They divide to form the keratinocytes of the stratum spinosum, which migrate superficially. Other types of cells found within the stratum basale are melanocytes (pigment-producing cells), Langerhans cells (immune cells), and Merkel cells (touch receptors).